1. Field of the Invention
The present invention relates to a novel method for controlling gene expression using Escherichia coli lactose repressor gene with a temperature-sensitive mutation. The present invention also relates to a method for gene expression using said method for controlling the gene expression, and more particularly to a method for controlling gene expression by controlling a temperature for culturing host cells.
2. Related Art
An expression control gene region of E. coli lactose operon, i.e., a gene region from a lac gene coding for a repressor protein to promoter/operator is one of the control gene regions which is most frequently used for the expression of a gene located downstream of the control gene region. This is because, when an inducer substance such as isopropyl-.beta.-D-thiogalactopyranoside (IPTG) exists in host cells, lactose repressor cannot bind to the lactose operator region and transcription from the lactose promoter occurs, which makes transcriptional control during the gene expression possible.
Various cloning vectors and gene expression vectors for the production of useful substances are used by virtue of the fact that a gene expression can be successfully carried out by addition of an inducer such as IPTG into a culture medium. For example, a member of the pUC series such as pUC18 etc. as a gene cloning vector, M13 phage series for determination of a nucleotide sequence of DNA, .lambda.gt11 etc. for cDNA cloning are used. Recently, this expression control system has been also used in studies using animal cells (Ulrich Deuschele et al., Proc, Natl. Acad. Sci. USA, Vol. 86, pp. 5400-5404, 1989; Mickey C. T. Hu et al., Mol. Cell. Biol. Vol. 10, pp. 6141-6151, 1990).
In addition, this expression control system has been used for the production of useful substances (Mercedes Zazo et al., Gene, Vol. 113, pp. 231-238, 1992). However, this system has drawbacks in that IPTG, an expensive inducing agent, must be added to the culture medium to induce the expression of genes. Especially, if this system is used for the production of useful substances on an industrial scale, the use of IPTG increases the production cost.
Accordingly, an industrially useful novel method for controlling the expression of a gene is urgently sought. Accordingly, regarding the expression of a desired gene, the development of a system for controlling the expression of a gene without using an expensive inducer such as IPTG, and of a method for expressing a gene using said control system are sought.